1. Field of the Invention
The invention relates to a motion-compensated field rate conversion, in which interpolated fields are obtained from input fields in dependence upon motion vectors.
2. Description of the Related Art
EP-A-0,475,499 discloses a system for field rate conversion in which the interpolated pictures result as shifted input fields. It is mentioned that, depending on the reliability of the motion vectors, the compensation can be more or less complete. In other words: if motion vectors are unreliable, their effect is reduced by multiplying them with a factor smaller than one. In the described case of a field rate doubler, the result is some 50 Hz motion judder which is not very objectionable and can be interpreted as a velocity depending blurring.
In field rate convertors with a higher or a non-integer ratio between the input and the output field rate, the effect of reduced motion compensation is the breakthrough of a much lower frequency in the motion judder. This frequency equals the largest common factor of the output and the input field rate. For example, an up-conversion from 24 Hz film material to 60 Hz video material, introduces a 12 Hz component in the motion judder. Apart from this long repetition period of the judder, the motion portrayal often is very irregular.